Tire temperature interpretation
 

What do you guys make of the tire temperatures and pressures listed below. These are from my 2003 Z06. I'm running 3 neg camber up front, and 1.5 in the rears. The tires were set to 31 psi cold (40 degrees ambient temp). The car has coil overs, bars, and has been corner weighted. No aero. The tires were brand new Hoosier R7s, 295 up front (11 inch wheel) and 315s in the back (12.5 inch wheel).

The car came hot off the track at big Willow, so the last two corners were rights, with more heat going into the outside (left side) tires.

Subjectively, the car felt awesome on these new (only scrubbed in) Hoosiers, very fast and beautifully adjustable.


Left front. 121 outside, 150 middle, 161 inside

Right front: 108 outside, 121 middle, 166 inside

Left rear: 168 outside, 171 middle, 173 inside

Right rear: 111 outside, 135 middle 169 inside

Cold pressure: 31 psi all around set at 40 degrees ambient temp.

Hot pressure: near 40 psi all around.

The fronts show a lot of negative camber with maybe a little toe out. Can't say whether that is too much or not but you might be able to knock a few tenths of a degree off your front camber and get a little better performance. Hoosier recommends -3.0 degrees for the R7 but that can be difficult to achieve on a C5. I tried for -2.3 on my C5s once I tried to go over -2.3 I found cross camber increased drastically and stock levels of positive caster became a faint goal.

It seems to me the right rear (Assuming left right really means right rear) alignment may need to be tweaked a little. Notice your left rear temps are fairly consistent across the tire which means the whole tire is working while the right rear has too much variation across the tread. Maybe a little less negative camber on the right rear would get that tire working better.

The Hoosier Guide for the R7s says your hot pressures are fine. However, I think your hot pressures are too high. I try to run lower hot pressures than those.

Bill

Thanks for the reply, Bill.

Yeah, the left rear looks just fine to me, with a pretty even temperature spread across the tire. That tire takes a lot of heat at Willow just before you come off the track, so it's nice to see that things seem to be working well with that tire.

However, as you say, the right rear tire has a range of 58 degrees across the tire. Likewise, the right front tire also has a large temperature spread--58degrees across the tire. The left front has a 40 degree spread. From what I understand, there should not be more than a 10 degree range across the tire. The temperatures are also a little low, but that may just be because it was such a cold day and the tires cooled off quickly.

So, I'm confused why only one tire has a nice temperature spread but the others don't. The alignment was done 2 months ago but a highly reputable race shop. I'm running the same specs as the Spec Corvette guys, and I have the same suspension as they do.

I agree that the pressures are a little high. I dropped them for the next session.

tire temps
 

Agree with Bill.
I would double check your front camber settings.
Hoosier R7's should definitely be started (cold) at lower temps. Around 26PSI, and possibly lower once you get good temp readings and verify camber settings. I am assuming you are running about 1/16" to 1/8" max toe out.
I generally found that an approximate 20 degree difference from inside to outside generally seemed to work well. Obviously track and driving style affect this. The general suspension setup used by Oli and most Spec Corvette guys should get you pretty close requiring only minor adjustments.
Note: Most racers have some camber gauge and toe plates at track events you could probably borrow to verify your settings. Just make sure you are on a level surface.
I am assuming you are using a probe gauge to check temps and not an infrared tool.

Tire temp as a tuning tool has been going out of favor over the past several years due to the difficulties in getting good info.
Did you come off of a hot lap or take a cool down? Are you using proper pin type probe poked under the surface to get a true read on the tire core temp? Are you measuring yourself or do you have help? There is usually enough variability in measuring temps to cause you to chase your tail.
I can't imagine how much the low ambient temps would affect that. If you look at the left rear tire temp as the only one with high temps on the outside that probably shows you you're not getting worthwhile info for any other position.

A better method would be recording accurate alignment settings
Mounting external cameras to see that the tires basically have enough camber
Using a G meter or good data acquisition to measure max steady state Gs in a corner and varying camber setting to get more or less Gs

The goal would be to observe and measure directly what you are trying to improve rather than a proxy with a high degree of variability, like tire temp.

You didn't mention if you changed the A arm bushings, as stock bushings flex a ton and require more static camber to compensate.
Isn't 40 psi hot a bit on the high side for a Hoosier?

Just to clarify, I came hot off the track, tried to use mostly engine braking to slow down, and then immediately got the temps using a quality pin-type probe.
I just had all the stock bushings replaced with the bushings used in the Spec Corvette suspension kit, and then took the car to the alignment shop used by Oli and other Spec Corvette racers.

At a glance it looks like the rear is close, but the front has too big a spread.

Not trying to cast doubt, but was the sticker a person whose done this a good bit and can consistently get repeatable numbers? I've found on the stick-type probes that (much like a durometer) there is some technique to it and folks without a good bit of experience can give some erroneous readings.

With DA systems and IR sensors really coming down in price, doing real-time temps is (in my opinion) the way to do it. Knowing what the surface temps are when the car is loaded in the actual corner goes way beyond carcass temps taken quite a while after the fact. I've had enough folks ask (and being an FSAE helper, the kids go through this every year) so I put together a primer that you might find helpful.

http://www.witchdoctormotorsports.com/ch192.htm

Here is a video that has a 3-sensor overlay for the RF tire. Just below the speedo it shows "in" for inboard, "mid" for middle and "out" for outboard relating to the sensors that cover the RF tire. I only have 3 sensors. Pretty interesting to see how quick the tires add/lose temp based on the driving.
Costas
cars and such...

That's pretty cool! I would love to have dynamic tire temp data like that on my data logger.

A little off topic, but I just finished reading, "Chevrolet = Racing? Fourteen Years of Raucous Silence," an engineer's account of how Chevy was covertly involved in race-car development in the late 60s. What really surprised me was that these Chevy engineers developed data logging as far back as then. They used wheel-speed sensors rather than GPS, of course. What was even more surprising was that they then plugged this data into a computer and were able to develop a car simulator. Pretty wild for 1960s technology. Can you imagine the size of their computer?!